A seat belt system for restraining an occupant of a vehicle ordinarily includes seat belt webbing, a buckle and a retractor. A locking tongue is connected to the webbing and is releasably lockable in the buckle when the webbing is extended around the vehicle occupant. The retractor includes a spool upon which the webbing is wound. The spool in the retractor rotates in an unwinding direction when the vehicle occupant withdraws the webbing from the retractor and moves the webbing toward the extended position in which the tongue is locked in the buckle. When the tongue is subsequently unlocked and released from the buckle, a rewind spring in the retractor rotates the spool in a winding direction to draw the webbing back into the retractor, and thus to move the webbing back from the extended position to a retracted position.
When the vehicle experiences a collision, the vehicle decelerates and the vehicle occupant wearing the seat belt webbing moves forcefully against the webbing. The force which is then applied to the webbing by the vehicle occupant urges the webbing to move outward from the retractor. Therefore, a retractor in a seat belt system ordinarily includes an emergency locking mechanism which blocks rotation of the spool in the unwinding direction upon the occurrence of vehicle deceleration indicative of a collision. The emergency locking mechanism thus prevents the webbing from being further withdrawn from the retractor when the vehicle experiences a collision.
It is sometimes desirable to prevent the webbing from being further withdrawn from the retractor throughout the time that the webbing is secured around the vehicle occupant, i.e., to maintain the webbing in a cinched condition. For example, it is often desirable to maintain the webbing in a cinched condition in a child seat belt system. A child seat belt system having means for maintaining the webbing in a cinched condition is disclosed in co-pending U.S. patent application Ser. No. 117,604, filed Sep. 7, 1993, now U.S. Pat. No. 5,398,997 entitled "Seat Belt System with Buckle-Responsive Retractor Lock," and assigned to TRW Vehicle Safety Systems Inc. In that system, two tongues are connected to the webbing to secure two respective sections of the webbing in positions extending around a seated child. The retractor is locked to prevent rotation of the spool in the unwinding direction in response to locking of the two tongues in a buckle.